1. Field of the Invention
The present invention relates to a propeller for a vessel propulsion apparatus that propels a vessel and a vessel propulsion apparatus including the same.
2. Description of the Related Art
A vessel propulsion apparatus such as an outboard motor generates thrust by rotating a propeller member provided with a plurality of blades.
The propeller member may be attached to a propeller shaft via a propeller damper that is elastically deformable. The propeller damper transmits a torque between the propeller member and the propeller shaft, and absorbs a shock between the propeller member and the propeller shaft. A shock (soft shock) caused by connection or disconnection of a dog clutch and a shock caused by a collision between the propeller member and an obstacle in water are absorbed by the propeller damper.
U.S. Patent Application Publication No. 2011/212657 A1 discloses an outboard motor including a propeller. The propeller includes a bushing spline-coupled to the propeller shaft, a propeller damper (main and sub dampers) disposed around the bushing, and a propeller member surrounding the bushing via the propeller damper. The bushing is disposed between a front spacer and a rear spacer surrounding the propeller shaft. The front spacer, the bushing, and the rear spacer are fixed to the propeller shaft by a nut attached to the propeller shaft.
When the propeller shaft is driven to rotate by an engine while the propeller is in water, the propeller damper elastically deforms, and the propeller member and the propeller shaft rotate relative to each other by an angle corresponding to the deformation amount. Then, when the elastic deformation amount of the propeller damper reaches a predetermined value, teeth provided on the rear spacer come into contact with the inner surfaces of the notches provided on the inner cylinder of the propeller member, and the propeller member and the propeller shaft rotate integrally. Accordingly, a torque is efficiently transmitted from the propeller shaft to the propeller member.
One of the indexes showing performance of the propeller damper is a maximum operating angle (maximum value of an operating angle). The operating angle is an elastic deformation amount of the propeller damper in the circumferential direction (relative rotation angle of the propeller member and the propeller shaft) when a torque to rotate the propeller member and the propeller shaft relative to each other is generated. The larger the maximum operating angle is, the larger the allowable relative rotation of the propeller member and the propeller shaft is, so that the function to absorb a shock caused by torque fluctuation is also improved. Therefore, a larger maximum operating angle is more preferable. Accordingly, the maximum operating angle is set to a value as large as possible in a range not larger than an operating angle that is slightly smaller than a limit operating angle, that is, an operating angle that causes breakage, etc., of the propeller damper.
In the conventional outboard motor described above, the propeller damper is held by the bushing, and teeth corresponding to a stopper are provided on the rear spacer. The propeller damper deforms in the circumferential direction until the teeth of the rear spacer come into contact with the inner surfaces of the notches of the propeller member. That is, an angle when the teeth of the rear spacer come into contact with the inner surfaces of the notches of the propeller member corresponds to the maximum angle of the relative rotation of the propeller member and the propeller shaft. This means that if the positional relationship between the rear spacer and the bushing in the circumferential direction changes, the maximum angle of the relative rotation of the propeller member and the propeller shaft changes.
However, both of the bushing and the rear spacer are spline-coupled to the propeller shaft. The position of the rear spacer with respect to the propeller shaft in the circumferential direction changes according to variations in dimensions of the spline hole and the spline shaft. Hence, the positional relationship between the rear spacer and the bushing in the circumferential direction changes according to variations in dimensions of the spline hole and the spline shaft. Therefore, the maximum operating angle is set so as not to exceed the limit operating angle by considering maximum values of the variations in dimensions. Therefore, variations in dimensions are a factor that hinders improvement in the performance of the propeller damper.